(a) Field of the Invention
The present invention relates to a coating composition. More particularly, the present invention relates to a composition capable of forming a plastic film which exhibits high hardness and excellent processability.
This application claims the benefit of Korean Patent Application No. 10-2013-0028140, filed on Mar. 15, 2013 and Korean Patent Application No. 10-2014-0029032, filed on Mar. 12, 2014, which are all hereby incorporated by reference in their entireties into this application.
(b) Description of the Related Art
With the advance of mobile appliances such as smart phones, tablet PCs or the like, substrates for displays have recently been required to become lighter and slimmer. Display windows or front panels of such mobile appliances are generally made of glass or reinforced glass both of which have excellent mechanical properties. However, glass suffers from the disadvantage that its own weight makes mobile appliances heavy and it is easily broken by an external impact.
As an alternative to glass, plastic resins have been studied. The plastic resin films are light in weight and resistant to impact, and thus are consistent with the trend of pursuing lighter mobile appliances. Particularly, to achieve a film with properties of high hardness and wear resistance, it is proposed to utilize a film in which a support substrate is coated with a hard coating layer.
Increasing the thickness of the hard coating layer is considered as an approach to improving the surface hardness thereof. The hard coating layer should be of a predetermined thickness to ensure the surface hardness sufficient as the alternative to glass. However, as the hard coating layer increases in thickness, the surface hardness thereof may become higher, but the hard coating layer is more prone to setting shrinkage which leads to wrinkling or curling with the concomitant production of cracks or exfoliations, and thus the coating layers are difficult to employ in practice.
Recently, some methods have been proposed for conferring a high hardness on hard coating films, without the problems of cracking and setting shrinkage-induced curling.
Korean Patent Publication No. 2010-0041992 discloses a plastic film composition, free of monomers, including a binder resin based on ultraviolet-curable polyurethane acrylate-based oligomers. However, this plastic film has a pencil hardness of about 3H, and thus the strength thereof is not sufficient to be a substitute for glass panels for displays.